My tub was leaking from under the tub. I believe it's called the 'drain shoe' and the gasket that was in place between 'drain shoe' and bottom of tub.

Took it all apart, and tried to put it back together.

However, for some reason, my drain basket - does not reach the threads on the 'drain shoe'. Upon deeper inspection, it appears that there was a ring (let's call it adapter - correct me if I'm wrong) with external and internal threads.

The drain basket threads the internals of the adapter and the externals of the adapter thread into the drain shoe.

So now, I've replaced all the necessary parts. I have the drain shoe, thread the adapter in like 2 threads, slip over the new gasket, push it up to bottom of tub, and from top of tub, I tighten the basket.

I get it tight and then 1/4 turn...POP! Adapter ring is on the bottom of the basket, and is no longer threaded to drain shoe.

Take the whole thing into a store that has a comprehensive line of plumbing supplies and get what you need.

Then, if it still leaks, there is always the plumber-school-dropout's friend: Silicone. Put silicone between ring and tub, not tightening too much so you have room for some silicone. Let it cure up a day before use.